We have two issues with our qapi union layout: 1) Even though the QMP wire format spells the tag 'type', the C code spells it 'kind', requiring some hacks in the generator. 2) The C struct uses an anonymous union, which places all tag values in the same namespace as all non-variant members. This leads to spurious collisions if a tag value matches a QMP name.
This patch is the back end for a series that converts to a saner qapi union layout. Now that all clients have been converted to use 'type' and 'obj->u.value', we can drop the temporary parallel support for 'kind' and 'obj->value'. Given a simple union qapi type: { 'union':'Foo', 'data': { 'a':'int', 'b':'bool' } } this is the overall effect, when compared to the state before this series of patches: | struct Foo { |- FooKind kind; |- union { /* union tag is @kind */ |+ FooKind type; |+ union { /* union tag is @type */ | void *data; | int64_t a; | bool b; |- }; |+ } u; | }; Note, however, that we do not rename the generated enum, which is still 'FooKind'. A further patch could generate implicit enums as 'FooType', but while the generator already reserved the '*Kind' namespace (commit 4dc2e69), there are already QMP constructs with '*Type' naming, which means changing our reservation namespace would have lots of churn to C code to deal with a forced name change. Signed-off-by: Eric Blake <ebl...@redhat.com> --- v10: rebase to earlier changes, match commit wording v9: new patch, but incorporates parts of v5 31/46 and Markus' RFC: http://lists.gnu.org/archive/html/qemu-devel/2015-10/msg02236.html --- scripts/qapi-types.py | 26 +++++--------------------- 1 file changed, 5 insertions(+), 21 deletions(-) diff --git a/scripts/qapi-types.py b/scripts/qapi-types.py index 579532d..d131430 100644 --- a/scripts/qapi-types.py +++ b/scripts/qapi-types.py @@ -148,23 +148,10 @@ struct %(c_name)s { if base: ret += gen_struct_fields([], base) else: - # TODO As a hack, we emit both 'kind' and 'type'. Ultimately, we - # want to use only 'type', but the conversion is large enough to - # require staging over several commits. - ret += mcgen(''' - union { - %(c_type)s kind; - %(c_type)s type; - }; -''', - c_type=c_name(variants.tag_member.type.name)) + ret += gen_struct_field(variants.tag_member.name, + variants.tag_member.type, + False) - # TODO As a hack, we emit the union twice, once as an anonymous union - # and once as a named union. Ultimately, we want to use only the - # named union version (as it avoids conflicts between tag values as - # branch names competing with non-variant QMP names), but the conversion - # is large enough to require staging over several commits. - tmp = '' # FIXME: What purpose does data serve, besides preventing a union that # has a branch named 'data'? We use it in qapi-visit.py to decide # whether to bypass the switch statement if visiting the discriminator @@ -173,7 +160,7 @@ struct %(c_name)s { # should not be any data leaks even without a data pointer. Or, if # 'data' is merely added to guarantee we don't have an empty union, # shouldn't we enforce that at .json parse time? - tmp += mcgen(''' + ret += mcgen(''' union { /* union tag is @%(c_name)s */ void *data; ''', @@ -182,17 +169,14 @@ struct %(c_name)s { for var in variants.variants: # Ugly special case for simple union TODO get rid of it typ = var.simple_union_type() or var.type - tmp += mcgen(''' + ret += mcgen(''' %(c_type)s %(c_name)s; ''', c_type=typ.c_type(), c_name=c_name(var.name)) - ret += tmp - ret += ' ' + '\n '.join(tmp.split('\n')) ret += mcgen(''' } u; - }; }; ''') -- 2.4.3